Growth of crystals, such as, for example, gallium nitride (GaN), may be accomplished via reactions and processing at high temperatures and/or high pressures. The reaction materials are generally placed inside a capsule, which is sealed and has an environment that is generally chemically inert and impermeable to solvents and gases that may be generated by the process or reactions occurring within the capsule. The capsule is subjected to high temperatures and the pressure in the capsule increases to the point that a material within the capsule forms a supercritical fluid, and crystal growth occurs under supercritical conditions. The pressure within the capsule may range anywhere from 1,000 pounds per square inch (psi) to 50,000 psi (about 70 bar to about 3,450 bar), and the temperature may range from about 300 to about 1,200 degrees Celsius. In some instances the pressure may need to be in the range of from about 70,000 to about 100,000 psi (about 4,800 bar to about 7,000 bar) and the temperature in the range of 500 to about 700 degrees Celsius to achieve commercially viable growth rates.